CN106368691B - Three-dimensional abnormal pore pressure prediction method based on rock physics seismic information - Google Patents
Three-dimensional abnormal pore pressure prediction method based on rock physics seismic information Download PDFInfo
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Abstract
The invention relates to a three-dimensional abnormal pore pressure prediction method based on petrophysical seismic information. Firstly, longitudinal wave velocity, transverse wave velocity and density parameters of petrophysics are applied to calculate the bulk modulus of a matrix of a lithologic stratum, and the dry pore space rigidity is calculated by adding core geological analysis, so that the pore pressure coefficient is obtained, and the calculation of the abnormal pore pressure of the single-well stratum is realized; and then, obtaining three-dimensional longitudinal wave impedance, transverse wave impedance, Poisson's ratio and density data by applying a three-dimensional seismic reflection data volume and a three-dimensional prestack elastic wave impedance inversion method, and predicting the three-dimensional stratum abnormal pore pressure by referring to a calculation method of the single-well stratum abnormal pore pressure and an obtained empirical formula. The method applies the rock physical parameters indirectly obtained by two geophysical methods of well logging and earthquake to the prediction of the pore pressure of the abnormal stratum, is simpler than directly measuring the rock physical parameters from a laboratory, is more scientific than subjectively given parameters, and is more precise than singly calculating the post-stack earthquake velocity.
Description
Technical Field
The invention relates to the field of data processing methods for oil and gas exploration and development, which mainly utilizes geophysical information of logging earthquake and obtained petrophysical parameters to predict abnormal pore pressure of a stratum and provide services for exploration and development of oil and gas fields, such as oil and gas transportation accumulation analysis, preparation before well drilling and the like.
Background
Formation pressure and formation temperature are important basic parameters for oil and gas field development. The pressure and temperature of the formation in a hydrocarbon reservoir determine not only the properties of the hydrocarbon fluid, but also the manner in which the hydrocarbon field is developed, the technical characteristics and economic cost of hydrocarbon recovery, and the ultimate recovery rate.
The abnormal formation pressure environment is a general geological phenomenon of a hydrocarbon-containing basin, influences the existence and movement forms of underground fluid, and has direct effects on the generation, migration, aggregation and accumulation of oil and gas. The abnormal formation pressure is not only an important research problem of petroleum geology, but also an important technical problem which puzzles the well drilling engineering field for a long time, and brings great difficulties to the well drilling construction safety, the identification and evaluation of an oil-gas layer in logging and the protection of an oil layer. Therefore, in the process of oil and gas exploration and development, the research and prediction of the abnormal formation pressure not only has theoretical significance, but also is actually needed.
However, the formation mechanism and the influence factor of the abnormal formation pressure are many, the research at home and abroad is continuously and deeply carried out, and an ideal method for accurately predicting and monitoring the abnormal formation pressure is not found at present. Abnormally high pressures have been encountered in drilling wells as early as the 30's of the 20 th century and they were recognized as the primary cause of many drilling accidents. However, this phenomenon has not been systematically studied until the 60's of the 20 th century (Fertl, 1976; Magara, 1978). The earliest quantitative pressure predictions were made by Hottman and Johnson (1965), which created a method of formation pressure prediction and monitoring using the resistivity and sonic time difference log data from previous wells, and found that formation pressures could not be predicted with full accuracy using the equivalent depth method alone, and in some formations appropriate empirical relationships had to be established. Forster and Whalen (1966) further discuss an equivalent depth method and an effective stress method, analyze feasibility and existing problems of pressure prediction and monitoring from the compaction of mudstone, and lay the foundation for quantitatively calculating the formation pore pressure. Subsequently, various data from drilling, logging, and logging that reflect changes in formation porosity and rock properties have been attempted for predicting and monitoring formation pressure (Boatman, 1967; Matthews and Kelly, 1967; Fertl, 1976; Magara, 1978). Bingham (1964) recognized that the factors affecting drilling speed come from the formation, the drilling tool and the drilling process, suggesting a correlation that should exist between drilling speed, rotational speed of the rotary table, weight on bit and bit size. Jorden and Shirley (1966) further developed Bingham's work to propose a d-exponential method for calibrating drilling rate, and later developed a dc-exponential method via improvements of Rehn and McColendon (1971). Pennebaker (1968) notes that seismic data is important information for pressure prediction, and it is considered that the key point of using seismic data prediction is how to correctly obtain depth and pressure values of abnormal formation pressure. They used seismic interval velocity data to predict formation pressures in the gulf of mexico in the united states, with predictions that are quite similar to actual mud weights used. Eaton (1972) analyzed and summarized the work of the predecessor in detail, proposed the concept of overburden pressure and formation pressure variation with burial depth, and established the pore pressure relation of shale resistivity, dc index and acoustic wave time difference based on the effective stress equation, namely the well-known Eaton method. With the advancement of seismic methods, seismic data have found widespread use in pressure prediction in the 80 th 20 th century (Bellotti and Giacca, 1978; Dobrinin and Serebryakov, 1989). The use of seismic information is not limited to interval velocities, but rather to comprehensive analysis and processing of seismic data volumes, predicted by specific properties in terms of seismic wave velocity and amplitude, etc. (Grauls et al, 1995; Djevanshirr and Akhnerdiev, 1998). The domestic fan Honghai (2005) provides a new method for solving formation pore pressure on the basis of analyzing and summarizing the commonly used traditional methods, namely an Eaton method and a dc index method. The method is characterized in that an empirical model describing the functional relation between the acoustic velocity of the argillaceous sediments and the vertical effective stress is established, and seismic layer velocity data are utilized in the actual prediction process.
Formation pore pressure prediction methods can be basically classified into three categories: well logging data analysis and prediction method, well drilling data analysis and prediction method and seismic information analysis and prediction method. Logging and well drilling are prediction after or in the process, and earthquake is prediction in advance. The prior application of seismic information prediction mainly aims at seismic interval velocity (longitudinal wave), and now due to the combination of the technical progress and logging information, the seismic information can be converted into rock physical parameters possibly, and more seismic information can be applied to stratum pore pressure prediction. The method is based on the fact that the stratum pore pressure prediction technology is advanced by one step.
Disclosure of Invention
The invention provides a three-dimensional abnormal pore pressure prediction method based on petrophysical seismic information by using logging and earthquake, which overcomes the defects of the conventional method for predicting the abnormal pore pressure of a stratum by using a laboratory petrophysical data formula, a subjective experience data formula or a post-stack seismic velocity data formula.
The technical scheme of the invention is as follows.
A three-dimensional abnormal pore pressure prediction method based on rock physics seismic information includes the steps of firstly, applying longitudinal wave velocity, transverse wave velocity and density parameters of rock physics, comprehensively analyzing and intersecting, establishing an empirical formula of a relation between the actually measured longitudinal wave velocity and density under a non-drainage saturated state and the formation matrix longitudinal wave velocity, and calculating the volume modulus k of the lithologic formation matrix0Adding core geological analysis to calculate the dry pore space rigidity kφFurther, the pore pressure coefficient B is obtained, and the calculation of the abnormal pore pressure of the single well stratum is realized; and then, obtaining three-dimensional longitudinal wave impedance, transverse wave impedance, Poisson's ratio and density data by applying a three-dimensional seismic reflection data volume and a three-dimensional prestack elastic wave impedance inversion method, and predicting the three-dimensional stratum abnormal pore pressure by referring to a calculation method of the single-well stratum abnormal pore pressure and an obtained empirical formula.
The technical scheme of the invention further comprises the following steps:
the bulk modulus k of the stratum matrix is obtained by applying longitudinal wave velocity, transverse wave velocity and density parameters of rock physics0The method comprises the following steps:
1) using longitudinal wave velocity V of multiple wellspAnd intersecting with the rho value of the density, and fitting an empirical formula of the relation between the density and the longitudinal wave velocity: ρ ═ f (V)p)；
2) Solving the porosity formula by using acoustic logging and density logging to solve the longitudinal wave velocity of the stratum skeleton
And density (p)m)；
Solving a porosity formula by sound waves:
density porosity formula:
formation porosity:
obtained from (1), (2) and (3):
Δtm(ρ-ρf)+ρm(Δtf-Δt)-(ρΔtf-ρfΔt)＝0
3) bulk modulus k of formation matrix0Obtaining:
wherein: wherein: rhof、ΔtfRespectively pore fluid density and acoustic wave velocity,
for measured formation acoustic velocity, ρ is measured formation density, ρm、VpmRespectively, the density of the stratum skeleton and the velocity of longitudinal waves, VsIs the shear wave velocity.
Formation pore space stiffness kφThe calculation of (1) comprises the calculation of the rigidity of four types of pore spaces of a spherical cavity seam hole, a coin-shaped gap, a needle-shaped gap and a two-dimensional tubular crack type, and the rigidity of the formation pore space formed by the sum of the rigidity of the four types of pore spaces
Is calculated byThe specific calculation steps are as follows:
1) void space stiffness of ball cavity voids
2) Rigidity of pore space of coin-shaped gap
3) Rigidity of pore space of needle-like gap
4) Pore space stiffness of two-dimensional tubular fractures
Following the estimation of Hill mean modulus, the formation total pore space stiffness:
wherein: w (x) is a weight parameter, w (x)1)+w(x2)+w(x3)+w(x4)＝1，K0Is the bulk modulus of the formation matrix, v is the Poisson's ratio, a<<c, c is the radius of the coin, and a is the thickness of the coin.
The calculation of the single-well pore pressure coefficient B and the formation abnormal pore pressure is specifically divided into the following steps:
1) pore pressure coefficient of single well B
The ratio of the change in pore pressure dP to the change in applied compressive stress d σ is referred to as the pore pressure coefficient B
Knowing the formation pore space stiffness KφBulk modulus of formation matrix K0And bulk modulus K of pore fluidfThe pore pressure coefficient B can be obtained;
2) pore pressure:
dP＝Bdσ
3) abnormal pore pressure coefficient
The abnormal pore pressure coefficient is defined as the ratio of pore pressure to hydrostatic pressure, i.e.:
if the horizontal direction of the compressive stress is zero and only the overlying formation gravity pressure exists, then:
wherein: rhowIs the hydrostatic density of the ground, p(z)Z is the vertical burial depth, which is the formation density.
The method firstly obtains rock physical parameters from well logging data of a drilled well, avoids the Biot (Biot-Willis) coefficient which is difficult to determine, calculates the formation abnormal pore pressure through an actual rock parameter fitting formula, then applies the prestack elastic wave impedance inversion technology to convert seismic geophysical information into rock physical parameter information, and predicts the formation abnormal pore pressure of a region ready for drilling or without drilling. The method applies the rock physical parameters indirectly obtained by two geophysical methods of well logging and earthquake to the prediction of the pore pressure of the abnormal stratum, is simpler and lower in cost than the method of directly measuring the rock physical parameters from a laboratory, is more scientific than subjectively given parameters, and is more precise than the method of singly calculating the seismic velocity after the stacking.
Drawings
FIG. 1 is a flow chart of a three-dimensional abnormal pore pressure prediction method based on petrophysical seismic information
FIG. 2 is a calculation curve of the abnormal pore pressure of the formation at a single well point
FIG. 3 shows the spatial distribution of three-dimensional abnormal pore pressure in a certain area
Detailed Description
As shown in fig. 1, the implementation of the present invention is mainly divided into the following steps:
(1) the method comprises the steps of comprehensively analyzing well-drilled well logging data, lithology, rock electrical characteristics, geological stratification and the like, and obtaining geophysical parameters (acoustic longitudinal wave velocity, transverse wave velocity and density) and other information of rocks at a well point. The longitudinal wave velocity and the density of the multiple wells are intersected, and an empirical relation between the longitudinal wave velocity and the density is established.
(2) The formula of porosity is obtained by utilizing acoustic logging and density logging, and the acoustic velocity and density of the stratum skeleton are reversely obtained, so that the volume modulus K of the stratum matrix is obtained0。
(3) Combining well point pore type composition and components, applying a stress to solve a pore space rigidity formula, and calculating to obtain formation pore space rigidity Kφ。
(4) Knowing the bulk modulus of the fluid, the formation matrix modulus K0And formation pore space stiffness KφThe pore pressure may be calculated according to a pressure formula and then an abnormal pore pressure curve for the well point may be calculated.
(5) Analysis of a three-dimensional seismic data volume. It is desirable to provide a relative amplitude preservation process, a three-dimensional seismic reflection data volume after prestack migration imaging and a prestack CRP imaging gather.
(6) The well-drilled synthetic record is calibrated, the well-earthquake relation is established, and the geological significance is accurately given to the earthquake.
(7) According to the technical requirements of the prestack elastic wave impedance inversion method, the prestack CRP imaging gather is reasonably divided into three parts of angle superposition data, and prestack wave impedance inversion is carried out. And finally, obtaining data bodies with higher quality such as longitudinal wave impedance, transverse wave impedance, density, Poisson ratio and the like.
(8) And (4) calculating the abnormal pore pressure of the whole three-dimensional body by using data volume data such as longitudinal wave impedance, transverse wave impedance, density, Poisson's ratio and the like according to the steps (2), (3) and (4), so as to realize prediction.
The specific technical scheme based on the above embodiment is as follows.
The first is the calculation of the pore pressure of the abnormal formation of the drilled single well. The method specifically comprises the following steps:
1) the collection and comprehensive analysis of the geological data and logging data of the drilled well are used for researching the petrophysical parameters (longitudinal wave velocity, transverse wave velocity and density) necessary for calculating the abnormal pore pressure of the stratum and the relation between the petrophysical parameters and the lithologic pore of the stratum.
2) Bulk modulus K of formation matrix0And (4) calculating.
a. Using longitudinal wave velocity V of multiple wellspAnd intersecting with the rho value of the density, and fitting an empirical formula of the relation between the density and the longitudinal wave velocity: ρ ═ f (V)p)。
b. Solving the porosity formula by using acoustic logging and density logging to solve the longitudinal wave velocity of the stratum skeleton
And density (p)m)。
Solving a porosity formula by sound waves:
density porosity formula:
formation porosity:
obtained from (1), (2) and (3):
Δtm(ρ-ρf)+ρm(Δtf-Δt)-(ρΔtf-ρfΔt)＝0
wherein: rhof、ΔtfRespectively pore fluid density and acoustic wave velocity,
for the measured formation acoustic velocity, ρ is the measured formation density.
(if there is a formation skeleton longitudinal wave velocity)
And density (p)m) The volume modulus K of the stratum matrix can be directly calculated by a measuring plate0(ii) a If there is measured formation porosity
Directly solving the longitudinal wave velocity of the stratum skeleton by the formulas (1) and (2)
And density (p)m)。)
c. Bulk modulus K of formation matrix0Obtaining:
wherein: rhom、VpmRespectively, the density of the stratum skeleton and the velocity of longitudinal waves, VsIs the shear wave velocity.
3) Formation pore space stiffness kφIs calculated by
The pores of a typical formation can be divided into four types: spherical cavity slot, coin shaped slot, needle shaped slot and two dimensional tubular slot types. Formation pore space stiffness KφIs the sum of the spatial stiffness of these four types of pores. The four types of pores respectively account for the total pore volume, and the pore volume is determined by mainly combining the geological characteristics, the core analysis and the logging information of a specific work area. The specific calculation steps are as follows:
a. ball cavity seam hole
Wherein: k0The volume modulus of the stratum matrix is shown, and v is Poisson's ratio.
b. Coin shaped gap
Wherein: a < < c, c is the radius of the coin circle, and a is the thickness of the coin.
c. Needle-like gap
d. Two-dimensional tubular fracture
Following the estimation of Hill mean modulus, the formation total pore space stiffness:
wherein: w (x) is a weight parameter, w (x)1)+w(x2)+w(x3)+w(x4)＝1
4) Calculation of pore pressure of abnormal formation of single well
a. Calculation of single well pore pressure coefficient B
The ratio of the change in pore pressure dP to the change in applied compressive stress d σ is referred to as the pore pressure coefficient (also known as the Skempton coefficient), and is generally denoted by B.
Knowing the formation pore space stiffness KφBulk modulus of formation matrix K0And bulk modulus K of pore fluidfSo as to obtain the pore pressure coefficient B
b. Pore pressure:
dP＝Bdσ
c. abnormal pore pressure coefficient
The abnormal pore pressure coefficient is defined as the ratio of pore pressure to hydrostatic pressure, i.e.:
if the horizontal direction of the compressive stress is zero and only the overlying formation gravity pressure exists, then:
wherein: rhowIs the hydrostatic density of the ground, p(z)Z is the vertical burial depth, which is the formation density.
Then, the three-dimensional seismic reflection data volume after seismic data processing such as seismic relative amplitude preservation processing and prestack migration imaging is applied, the relationship between the earthquake and the logging is established through calibration of synthetic records, the stratum is expressed by a geophysical language together, three-dimensional prestack elastic wave impedance inversion is carried out under the constraint of logging elastic acoustic wave impedance and density parameters, and finally prediction of three-dimensional stratum abnormal pore pressure is achieved. The method comprises the following specific steps:
1) calibration of synthetic records
And the synthetic record calibration is to calculate a reflection coefficient curve by utilizing an acoustic logging curve and a density curve, then convolute the reflection coefficient curve with the selected seismic wavelets to form an artificial synthetic seismic record, and then match the artificial synthetic seismic record with the well side seismic record.
The principle of calibration of the synthetic record is as follows: the synthetic record is basically consistent with the characteristics of the reflected wave group of the seismic section, and the wave forms are similar; the sign of the logging information, the geological stratification of the target layer and the reflected wave group of the seismic section have good corresponding relation; on the multi-well connected well section, the target layer layered measurement depth of each well is correspondingly unified with the time scale of the seismic section reflection wave group at the corresponding position.
One of the main factors affecting the correspondence of the synthesized recorded wave sets is wavelets. Wavelet extraction and synthetic record making are carried out interactively, wavelets are extracted from a target interval, synthetic record calibration is carried out by using wave group characteristics as a mark layer, and a time-depth relation curve is reasonably corrected, so that the synthetic record and a well-side seismic channel have good corresponding relation, the maximum correlation is realized, geological stratification and a seismic interpretation horizon are correspondingly consistent, and an initial time-depth relation is obtained. On the basis, wavelets are obtained by using a least square method by using the well-side seismic channels and the initially calibrated impedance curve, then synthetic records are made again by using the extracted wavelets, and then the layer position calibration is carried out, and the steps are repeated until wavelets which are relatively stable, have reasonable time-depth relation and have good correlation between the earthquake and the synthetic records are obtained.
2) Three-dimensional prestack elastic wave impedance inversion
The prestack elastic wave impedance inversion is performed on prestack gather data (prestack CRP gather data or partial stack data) after seismic data processing. The method is a complex Zoeppritz matrix equation established based on the reflection and transmission theory of seismic waves on an elastic interface, the seismic reflection and transmission coefficients are not only related to the incident angle and the transmission angle, but also related to elastic parameters of longitudinal waves, transverse waves, density and the like of an upper rock stratum and a lower rock stratum, and the relationship between the seismic reflection and transmission coefficients is very complex. Through different simplified approximations of the Zoeppritz matrix equation, an approximate function relation expression of the elastic wave impedance and four variables of longitudinal wave velocity, transverse wave velocity, rock density and incidence angle is obtained:
wherein: k ═ beta2/α2(ii) a α represents a longitudinal wave velocity; β represents the shear wave velocity; ρ represents a density; theta denotes an incident angle
Therefore, the prestack inversion involves 4 parameters of longitudinal wave, transverse wave, density and incidence angle.
The main contents of the three-dimensional prestack elastic wave impedance inversion are as follows:
a. quality analysis and pre-processing of prestack gathers
The quality analysis research of the prestack CRP gather data body researches the feasibility and the solution of prestack inversion on the premise of the existing data quality, and performs appropriate prestack CRP gather preprocessing.
Dividing and partially overlapping the pre-stack CRP gather data volume, generally dividing the pre-stack CRP gather data volume into three parts of a near track (small angle), a middle track (middle angle) and a far track (large angle) according to the offset (incident angle), and respectively overlapping to form three partially overlapped data volumes.
b. Logging data analysis and preprocessing
And collecting data of logging curves, oil testing, production testing, layering and the like of wells in the work area. And editing, controlling quality and standardizing the logging curve. And (4) carrying out statistical analysis on the change rules of the longitudinal wave speed, the transverse wave speed and the fluid property of various lithological properties of the target interval.
c. Petrophysical analysis, prestack CRP gather AVO, AVA feature analysis research
And performing AVO forward modeling according to the logging data, researching the relation between the amplitude and the incident angle of the AVO forward modeling gather, and analyzing by combining with the actual gather data to determine the AVO abnormal type. Correcting the density data and estimating the missing transverse wave data; completing the statistics of the relation between the reservoir and non-reservoir speed, density, lithology, fluid and porosity in the work area; and developing fluid replacement research to obtain rock elastic parameter results of stratum rocks under different water saturation conditions, establishing a regional rock physical explanation template, and completing establishment of the relationship between rock physical parameters and rock elastic parameters.
d. Fine borehole seismic calibration of different partial gather stacked data volumes
And carrying out fine synthesis record calibration on the well in the work area. And respectively performing wavelet estimation on the stacked seismic data volume of each part, and respectively calibrating the fine synthetic record. Different wavelets correspond to different stacked seismic data volumes, and differences are analyzed to find out characteristics and rules.
e. Establishment of three-dimensional structure control model
And (3) carrying out structural explanation on a main target layer, a control layer and a main large fault in the research area, and establishing a geological structure control model conforming to the actual underground geological deposition rule on the basis. And selecting a reasonable interpolation method to generate an in-well interpolation elastic wave impedance initial model meeting inversion requirements.
f. Prestack elastic wave impedance inversion
The prestack elastic wave impedance inversion is performed using a simplified approximation of the Zoeppritz matrix equation. And simultaneously carrying out simultaneous solution on a plurality of seismic data volumes after stacking at different angles or offset distances to generate rock elasticity parameter data volumes such as longitudinal wave impedance, transverse wave impedance, density, longitudinal-transverse wave velocity ratio and the like. And further obtaining elastic parameter data bodies such as Poisson's ratio, stratum volume modulus K and the like.
3) Prediction of three-dimensional formation abnormal pore pressure
With the rock elasticity parameter data bodies such as longitudinal wave impedance, transverse wave impedance, density, longitudinal and transverse wave velocity ratio and the like, the calculation can be carried out by imitating the calculation method of the pore pressure of the abnormal stratum of the single well.
Then, the pore pressure value of the abnormal stratum predicted by the well bypass is compared with the pore pressure value of the abnormal stratum calculated by actual drilling. Generally, as long as the longitudinal wave impedance, the transverse wave impedance and the density obtained by the prestack elastic wave impedance inversion are well matched with the longitudinal wave impedance, the transverse wave impedance and the density calculated by the well by-pass actual measurement, the well by-pass predicted abnormal formation pore pressure value is also well matched with the actual drilled and calculated abnormal formation pore pressure value. If the coincidence is poor, error analysis and correction are carried out, and the technical method is like iterative inversion of wave impedance.
FIG. 2 is a calculated plot of the anomalous pore pressure of the formation at a single well point as performed by an embodiment of the present invention. It indicates the variation of formation pore pressure with depth at the well site. The pressure coefficient is defined as the ratio of the actual formation pressure to the hydrostatic pressure at the same depth. Typically, a pressure coefficient of less than 1 indicates a negative formation pore pressure anomaly; between 1 and 1.27, indicating normal and abnormal; the pressure is between 1.27 and 1.5, and an overpressure abnormal transition zone is represented; the overpressure is between 1.5 and 1.73, which indicates overpressure abnormity; when greater than 1.73, a strong overpressure anomaly is indicated. In the drilling process, when the drilling meets an overpressure transition zone or an overpressure stratum or a strong overpressure stratum, measures are taken correspondingly to prevent drilling accidents.
FIG. 3 is a diagram of the prediction of the spatial distribution of abnormal pore pressure in a three-dimensional formation in a certain area according to an embodiment of the present invention. The method shows the distribution condition of the abnormal pore pressure of the three-dimensional space stratum in a certain area. Before exploration and drilling at a selected well position, the condition of abnormal pore pressure of the underground stratum at the well position can be predicted in advance by using the method, and preparation is made in advance to realize that a plurality of cores exist. Meanwhile, the method can also be used as important data for predicting oil and gas migration and accumulation.
Claims (3)
1. The three-dimensional abnormal pore pressure prediction method based on the rock physics seismic information is characterized by comprising the following steps: firstly, longitudinal wave velocity, transverse wave velocity and density parameters of rock physics are appliedComprehensively analyzing and intersecting, establishing an empirical formula of the relation between the longitudinal wave velocity and the density and the actually measured longitudinal wave velocity and the longitudinal wave velocity of the stratum matrix under the condition of non-drainage saturation, and calculating the bulk modulus k of the lithologic stratum matrix0Adding core geological analysis to calculate the dry pore space rigidity kφFurther, the pore pressure coefficient B is obtained, and the calculation of the abnormal pore pressure of the single well stratum is realized; then, obtaining three-dimensional longitudinal wave impedance, transverse wave impedance, Poisson's ratio and density data by applying a three-dimensional seismic reflection data volume and a three-dimensional prestack elastic wave impedance inversion method, and predicting the three-dimensional stratum abnormal pore pressure by referring to a calculation method of the single-well stratum abnormal pore pressure and an obtained empirical formula;
the calculation method of the abnormal pore pressure of the single-well stratum and the solved empirical formula are as follows:
the calculation of the single well pore pressure coefficient B and the formation abnormal pore pressure comprises the following steps:
1) pore pressure coefficient of single well B
The ratio of the change in pore pressure dP to the change in applied compressive stress d σ is referred to as the pore pressure coefficient B
Knowing the formation pore space stiffness KφBulk modulus of formation matrix K0And bulk modulus K of pore fluidfThe pore pressure coefficient B can be obtained;
2) pore pressure:
dP＝Bdσ
3) abnormal pore pressure coefficient
The abnormal pore pressure coefficient is defined as the ratio of pore pressure to hydrostatic pressure, i.e.:
if the horizontal direction of the compressive stress is zero and only the overlying formation gravity pressure exists, then:
wherein: rhowIs the hydrostatic density of the ground, p(z)Z is the vertical burial depth, which is the formation density.
2. The method for predicting three-dimensional abnormal pore pressure based on petrophysical seismic information as claimed in claim 1, wherein the bulk modulus k of the stratum matrix is obtained0The method comprises the following steps:
1) using longitudinal wave velocity V of multiple wellspAnd intersecting with the rho value of the density, and fitting an empirical formula of the relation between the density and the longitudinal wave velocity: ρ ═ f (V)p)；
2) Solving the porosity formula by using acoustic logging and density logging to solve the longitudinal wave velocity of the stratum skeleton
And density (p)m)；
Solving a porosity formula by sound waves:
density porosity formula:
formation porosity:
obtained from (1), (2) and (3):
Δtm(ρ-ρf)+ρm(Δtf-Δt)-(ρΔtf-ρfΔt)＝0
3) bulk modulus k of formation matrix0Obtaining:
wherein: rhof、ΔtfRespectively pore fluid density and acoustic wave velocity,
for measured formation acoustic velocity, ρ is measured formation density, ρm、VpmRespectively, the density of the stratum skeleton and the velocity of longitudinal waves, VsIs the shear wave velocity.
3. The method for predicting three-dimensional abnormal pore pressure based on petrophysical seismic information according to claim 2, wherein the rigidity k of the formation pore space isφThe calculation of (1) comprises the calculation of the rigidity of four types of pore spaces including a spherical cavity seam hole, a coin-shaped seam, a needle-shaped seam and a two-dimensional tubular seam, and the rigidity of the stratum pore space formed by the sum of the rigidity of the four types of pore spaces
The specific calculation steps are as follows:
1) void space stiffness of ball cavity voids
2) Rigidity of pore space of coin-shaped gap
3) Rigidity of pore space of needle-like gap
4) Pore space stiffness of two-dimensional tubular fractures
Following the estimation of Hill mean modulus, the formation total pore space stiffness:
wherein: w (x) is a weight parameter, w (x)1)+w(x2)+w(x3)+w(x4)＝1，K0Is the bulk modulus of the formation matrix, v is the Poisson's ratio, a<<c, c is the radius of the coin, and a is the thickness of the coin.
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